Bluetongue, an arthropod-borne viral disease, occurs in cattle, sheep, goats, and wild ruminants. Bluetongue lesions in affected animals resemble infectious bovine virus diarrhea, vesicular stomatitis virus, malignant catarrhal fever, mycotic stomatitis, rinderpest, photosensitization, and foot and mouth disease. Bluetongue virus (BTV) has been incriminated as a cause of hydranencephaly in cattle and of infertility, abortion, and birth of defective young in cattle and sheep. Twenty four serotypes are reported in the literature as causing problems ranging from inapparent infection to acute fulminating infection. Chronic, persistent virus shedding cattle have also been recognized. With BTV there is a marked loss of body condition and marketing of slaughter animals may be delayed. In BTV-infected sheep, wool growth may be impaired by the development of wool breaks which produce a defective or low yielding fleece. The marked debility following BTV infections may result in a lowering of resistance to secondary bacterial or chlamydial infections and other predatory factors. The reproductive efficiency of infected animals is also adversely affected.
Abortions and defective offspring are observed in infected animals, and some animals may be barren for one or more breeding seasons. The most significant damage inflicted by bluetongue infections is economic loss resulting from embargoes and stringent testing requirements imposed on producers who export cattle, cattle semen, and sheep from bluetongue endemic areas.
Under natural conditions, transmission of the virus occurs via the bites of at least four Culicoides species, e.g., sand flies, midges. The biological transmission of BTV between cattle and sheep by the same culicoid vector has been demonstrated experimentally (Luedke et al, 28 AJVR 457 (1967)). Cattle, sheep, and many species of wild ruminants may act as reservoirs of BTV producing a means for the virus to overwinter. A persistent BTV viremia, which can last as long as three years has been identified in cattle (Hourrigan, 51 Aust Vet J 170 (1975)). Once BTV becomes established in a country, the virus is virtually impossible to eradicate (Erasmus, 51 Aust Vet J 209). The etiologic agent of bluetongue belongs to the family Reoviridae, genus Orbivirus.
The viral etiology of bluetongue was established by Theiler in 1906, (Erasmus, 51 Aust V e t J 165 (1975)). Since then several reports have appeared in the literature which (a) confirm the isolation of bluetongue virus from cattle, sheep, goats, and a number of wild ruminants and (b) the clinical and pathological features of the bluetongue diseases, and (c) describe infections resulting from different BTV serotypes. For example, see Onderstepoort (J Vet Sci Anim Indus 7 (1944); Komarov and Goldsmit, Refuah Vet 96 (1951); Price and Hardy, 124 J Am Med Assn 255 (1954); Shope et al, 111 J Exp Med 155 (1960); Livingston and Hardy, 25 AJVR 1958 (1964); Luedke et al 30 AJVR 511 (1969); Hourrigan et al, 51 Aust Vet J 170 (1975), Immunological control of bluetongue in the United States was first attempted by McKercher et al 118 AJVR 310 (1975), with a BTV International serotype 10 vaccine grown in fertile hen eggs. This product was patterned after that of Alexander, (J V et Sci Indus 231 (1947)), who first succeeded in propagating the bluetongue virus in chicken embryos.
Early vaccination protocols were routinely carried out in South Africa and Israel using an egg-attenuated polyvalent live virus vaccine containing a number of bluetongue strains. An egg-adapted vaccine produced by Cutter Laboratories and used in the United States has been taken off the market because of severe reactions in vaccinated sheep. Subsequently, Kemeny and Drehle, 22 AJVR 921 (1961), adapted the BTV International type 10 from eggs to bovine kidney cell cultures. This modified live virus vaccine, produced by Colorado Serum Company, is used for sheep in the United States.
There is a need for improvements in development of vaccines for use in immunizing ruminants, in particular, sheep and lambs against Bluetongue virus. The present invention addresses this need. The citation of any reference herein should not be deemed as an admission that such reference is available as prior art to the instant invention.